Liquid discharge apparatus, liquid discharge method, and liquid discharge program

Abstract

To provide a liquid discharge device, a liquid discharge method, and a liquid discharge program capable of suppressing the occurrence of discharge failure in a nozzle of ink of a specific color.SOLUTION: In the liquid discharge device 1, the first discharge head 10A and the second discharge head 10B are arranged such that the position of a part of the first nozzle 14a and the position of a part of the second nozzle 14b overlap in the conveyance direction in the joint region 12c, and the controller 40 executes the risk acquiring processing of acquiring the information regarding the drying risk of the liquid in each of the nozzle 14a and 14b, the mask selecting processing of selecting one mask in accordance with the drying risk, and the printing processing of performing the printing by using the selected one mask based on the print job.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] The present disclosure relates to a liquid ejection device that ejects liquid, a liquid ejection method, and a liquid ejection program. [Background technology]

[0002] Conventionally, a liquid ejection device such as that described in Patent Document 1 has been known. This liquid ejection device has heads that eject inks of process colors such as cyan, magenta, yellow, and black, as well as heads that eject inks of special colors such as red, green, blue, and gold. Therefore, when printing based on image data of RGB values, it is possible to obtain a printed image that is highly reproducible to the image data. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2023-111540 Summary of the Invention [Problem to be solved by the invention]

[0004] However, spot color inks are generally used less frequently than process color inks and tend to dry out easily in the nozzles, which makes them prone to ejection problems.

[0005] Therefore, an object of the present disclosure is to provide a liquid ejection device, a liquid ejection method, and a liquid ejection program that can suppress the occurrence of ejection defects in nozzles for special color ink. [Means for solving the problem]

[0006] A liquid ejection device according to the present disclosure includes a first ejection head having a plurality of first nozzles for ejecting liquid, a second ejection head having a plurality of second nozzles for ejecting the liquid, a transport device that transports a recording medium relative to the first ejection head and the second ejection head in a transport direction, a moving device that moves the first ejection head and the second ejection head in a movement direction that intersects the transport direction, and a control device, wherein the first ejection head and the second ejection head are arranged such that, in a predetermined seam region, positions of some first nozzles among the plurality of first nozzles and positions of some second nozzles among the plurality of second nozzles overlap in the transport direction, and the control device The system executes a risk acquisition process that acquires information regarding the drying risk of the liquid in each of the first nozzles and the some of the second nozzles; a mask selection process that selects one mask in accordance with the drying risk from among a plurality of masks that are present in accordance with differences in the ratios, the mask determining the rate at which the number of nozzles used to eject liquid among the plurality of first nozzles that are aligned in the movement direction among the some of the first nozzles increases in one direction of the transport direction, and the rate at which the number of nozzles used to eject liquid among the plurality of second nozzles that are aligned in the movement direction decreases in one direction of the transport direction; and a printing process that performs printing using the selected mask based on a print job. [Effects of the Invention]

[0007] According to the liquid ejection device of the present disclosure, by changing the mask depending on the risk of drying, it is possible to prevent the ink in the nozzles in the joint area between the first ejection head and the second ejection head from drying, thereby suppressing the occurrence of ejection defects. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a schematic diagram showing the configuration of a liquid ejection device according to this embodiment. [Figure 2] FIG. 2 is a schematic diagram showing the configuration of a plurality of ejection heads mounted on a carriage. [Figure 3]FIG. 3 is a block diagram showing the configuration of the liquid ejection device. [Figure 4] FIG. 4A is a schematic diagram for explaining a normal mask, and FIG. 4B is a schematic diagram for explaining a special mask A. As shown in FIG. [Figure 5] FIG. 5A is a schematic diagram for explaining the special mask B, and FIG. 5B is a schematic diagram for explaining the special mask C. As shown in FIG. [Figure 6] FIG. 6 is a flowchart showing an example of the operation of the liquid ejection device in the printing process. [Figure 7] FIG. 7 is a flowchart showing an example of the mask setting process. [Figure 8] FIG. 8 is a flowchart showing another example of the mask setting process. [Figure 9] FIG. 9 is a flowchart showing another example of the mask setting process. [Figure 10] FIG. 10 is a flowchart showing another example of the mask setting process. [Figure 11] 11A and 11B are flowcharts showing another example of the mask setting process. [Figure 12] FIG. 12 is a flowchart showing another example of the mask setting process. [Figure 13] 13A to 13C are schematic diagrams for explaining the type of mask and the degree to which banding is noticeable when banding exists in a seam region due to misalignment in the front-to-rear direction between the first and second ejection heads. DETAILED DESCRIPTION OF THE INVENTION

[0009] A liquid ejection device, a liquid ejection method, and a liquid ejection program according to embodiments of the present disclosure will be described below with reference to the drawings. Note that the concept of direction used in the following description is used for convenience of explanation and does not limit the orientation of each disclosed configuration to that direction. Furthermore, the liquid ejection device described below is merely one embodiment of the present disclosure. Therefore, the present disclosure is not limited to the following embodiments, and additions, deletions, or modifications to the configuration are possible within the scope of the disclosure.

[0010] <Configuration of Liquid Ejection Device> Fig. 1 is a schematic diagram showing the configuration of a liquid ejection device 1 according to this embodiment. As shown in Fig. 1, the liquid ejection device 1 is a device that ejects a liquid such as ink from nozzles 14 (Fig. 2) of an ejection head 10 onto a recording medium A to form an image on the recording medium A. Below, an example in which the liquid ejection device 1 is applied to an inkjet printer will be described, but it can also be applied to other uses.

[0011] The liquid ejection device 1 is a serial head type and includes multiple ejection heads 10, a platen 20, multiple tanks 21, a transport device 22, and a moving device 23. The transport direction in which the recording medium A is transported by the transport device 22 is referred to as the front-rear direction. The moving direction that intersects with the transport direction is referred to as the left-right direction. The direction that intersects with both the transport direction and the moving direction is referred to as the up-down direction. However, the directions related to the liquid ejection device 1 are not limited to those described above.

[0012] The ejection head 10 includes two color heads 11, two special color heads 12, and two white background heads 13. Details of the ejection head 10 will be described later with reference to FIG.

[0013] The platen 20 is a plate-like member with a flat upper surface, and defines the distance between the recording medium A placed on its upper surface and the lower surfaces of the ejection heads 10 placed opposite it. The tanks 21 are containers that store liquid for each ejection head 10 via flexible tubes 24, and the tanks 21 are provided in numbers equal to or greater than the number of types of liquid. For example, the tanks 21 include a tank 21a that stores process color ink to be supplied to the color head 10a, a tank 21b that stores spot color ink to be supplied to the spot color head 10b, and a tank 21c that stores white ink to be supplied to the white head 10c.

[0014] Examples of process color inks include cyan, magenta, yellow, and black inks. Examples of special color inks are inks of colors different from the process colors, such as red, green, blue, and gold inks. Examples of background inks include white ink.

[0015] The transport device 22 has, for example, two pairs of transport rollers 25, 25 and a transport motor 26 (FIG. 3). The pair of transport rollers 25 is configured such that two rollers, each having a shaft extending in the left-right direction, are arranged one above the other. One of the rollers is connected to the rotation shaft of the transport motor 26 and rotates when driven by the transport motor 26. These two pairs of transport rollers 25, 25 are arranged spaced apart from each other in the front-to-rear direction, sandwiching the center position of the platen 20 therebetween. The recording medium A is sandwiched between the upper and lower rollers of each pair of transport rollers 25 and transported in the front-to-rear direction in response to the drive of the transport motor 26.

[0016] The movement device 23 includes a carriage 27, two guide rails 28, a movement motor 29 (FIG. 3), and an endless belt 30. The two guide rails 28 extend in the left-right direction above the platen 20, sandwiching the ejection head 10 between them in the front-rear direction. The carriage 27 carries the ejection head 10 and is supported by the two guide rails 28 so as to be movable in the left-right direction. The endless belt 30 extends in the left-right direction and is wound around pulleys 31, 31 arranged on either side of the platen 20. A portion of the endless belt 30 is connected to the carriage 27, and one of the pulleys 31 is connected to the rotation shaft of the movement motor 29. Therefore, when the movement motor 29 is driven, the endless belt 30 travels in the left-right direction, and the carriage 27 reciprocates in the left-right direction along the guide rails 28. This allows the ejection head 10 mounted on the carriage 27 to move in the left-right direction.

[0017] <Discharge head> 2 is a schematic diagram showing the configuration of multiple ejection heads 10 mounted on a carriage 27. As described above, the ejection head 10 includes two color heads 11, two spot color heads 12, and two white background heads 13. Specifically, the color heads 11 include a pair of a first color head 11a and a second color head 11b, the spot color heads 12 include a pair of a first spot color head 12a and a second spot color head 12b, and the white background head 13 includes a pair of a first white background head 13a and a second white background head 13b.

[0018] Of these, at least the first color head 11a and the first feature color head 12a constitute a first ejection head 10A according to the present disclosure, and the second color head 11b and the second feature color head 12b constitute a second ejection head 10B according to the present disclosure. Note that in the following description, the first white background head 13a is also included in the first ejection head 10A, and the second white background head 13b is also included in the second ejection head 10B.

[0019] In this embodiment, only a pair of first and second color heads 11a and 11b is illustrated as the color head 11, but if multiple types of ink are used as process color inks, it is sufficient to have a configuration including at least the same number of pairs of heads 11a and 11b as the number of types used. Similarly, in this embodiment, only a pair of first and second spot color heads 12a and 12b is illustrated as the spot color head 12, but if multiple types of ink are used as spot color inks, it is sufficient to have at least the same number of pairs of heads 12a and 12b as the number of types used.

[0020] Each ejection head 10 has a plurality of nozzles 14. The first ejection head 10A has a plurality of nozzle rows 15a in which a plurality of first nozzles 14a are arranged in the front-rear direction, and the plurality of nozzle rows 15a are arranged side by side in the left-right direction. The second ejection head 10B has a plurality of nozzle rows 15b in which a plurality of second nozzles 14b are arranged in the front-rear direction, and the plurality of nozzle rows 15b are arranged side by side in the left-right direction.

[0021] The first and second ejection heads 10A and 10B, which eject the same type of liquid, are positioned with a shift relative to each other in the front-to-back and left-to-right directions. Specifically, the first color head 11a is positioned to the left and rear of the second color head 11b. The heads 11a and 11b do not overlap each other in the left-to-right direction, but partially overlap each other in the front-to-back direction, forming a seam region (color seam region) 11c. In this seam region 11c, some of the first nozzles 14a of the first color head 11a (e.g., a predetermined number N of first nozzles 14a from the rear end) and some of the second nozzles 14b of the second color head 11b (e.g., a predetermined number N of second nozzles 14b from the front end) are arranged to overlap in the front-to-back direction.

[0022] The first spot color head 12a is located to the left of and behind the second spot color head 12b. The heads 12a, 12b do not overlap each other in the left-right direction, but partially overlap each other in the front-to-back direction, forming a seam region (spot color seam region) 12c. In this seam region 12c, some of the first nozzles 14a of the first spot color head 12a (e.g., a predetermined N number of first nozzles 14a from the rear end) and some of the second nozzles 14b of the second spot color head 12b (e.g., a predetermined N number of second nozzles 14b from the front end) are arranged to overlap in the front-to-back direction.

[0023] The first white background head 13a is located to the left of and behind the second white background head 13b. The heads 13a, 13b do not overlap in the left-right direction, but partially overlap in the front-to-back direction, forming a seam region (white background seam region) 13c. In this seam region 13c, some of the first nozzles 14a of the first white background head 13a (e.g., a predetermined number N of first nozzles 14a from the rear end) and some of the second nozzles 14b of the second white background head 13b (e.g., a predetermined number N of second nozzles 14b from the front end) are arranged to overlap in the front-to-back direction.

[0024] In the color seam region 11c described above, the first nozzles 14a and second nozzles 14b overlap each other when viewed left-right at a certain position in the front-rear direction, forming one nozzle row 17 extending left-right, and the color seam region 11c has multiple such nozzle rows 17. Each nozzle row 17 comprises the same number of first nozzles 14a and second nozzles 14b. The spot color seam region 12c and the white background seam region 13c also have multiple nozzle rows 17 similar to the above, and each nozzle row 17 comprises the same number of first nozzles 14a and second nozzles 14b.

[0025] The ejection head 10 described above has a flow path part made up of a stack of multiple plates, and a driving element 16. Recesses or through-holes are formed in each plate, and by stacking the plates, the flow path part has internal flow paths (for example, a common flow path and individual flow paths) through which liquid flows to each nozzle 14. The driving element 16 is an actuator such as a piezoelectric element, a heat generating element, or an electrostatic actuator. A driving element 16 is provided for each nozzle 14, and applies pressure to the liquid in the individual flow paths to eject the liquid from the nozzle 14.

[0026] <Other Configurations of the Liquid Ejection Device> Fig. 3 is a block diagram showing the configuration of the liquid ejection device 1. As shown in Fig. 3, the liquid ejection device 1 includes a control device 40, and a head drive circuit 50, a transport drive circuit 51, a movement drive circuit 52, a display device 53, an input device 54, a temperature sensor 55, a humidity sensor 56, and an imaging device 57, which are connected to the control device 40. In addition, an external device 60 that is not part of the liquid ejection device 1 can be connected to the control device 40 so as to be able to communicate with it via wire or wirelessly.

[0027] Of these, the control device 40 has a calculation unit 41, a storage unit 42, an interface 43, etc. The calculation unit 41 includes at least one circuit selected from the group consisting of a processor such as an MPU and an integrated circuit such as an ASIC. The calculation unit 41 controls the operation of each unit of the liquid ejection device 1 and executes various processes by executing a predetermined computer program. Details of each process will be described later.

[0028] The storage unit 42 is a memory accessible from the calculation unit 41, and includes a ROM and a RAM. The ROM stores computer programs (including the liquid ejection program according to the present disclosure) executed by the calculation unit 41, as well as data necessary for the calculation unit 41 to execute the computer programs. The RAM temporarily stores various data, such as image data received from the external device 60 and data generated by the calculation unit 41.

[0029] The interface 43 is a communication device for transmitting and receiving data via wire or wirelessly to and from the external device 60. The control device 40 can receive various data such as image data from the external device 60 via the interface 43. Examples of the external device 60 include other computers, cameras, communication networks, recording devices, displays, and printers.

[0030] The control device 40 is connected to the drive elements 16 via a head drive circuit 50. The control device 40 outputs a control signal to the head drive circuit 50, and the head drive circuit 50 generates a drive signal based on the input control signal and outputs it to each drive element 16. Each drive element 16 is driven based on the input drive signal to apply a discharge pressure to the liquid in the individual flow path.

[0031] The control device 40 is connected to the conveyance motor 26 via a conveyance drive circuit 51. The control device 40 outputs a control signal to the conveyance drive circuit 51, and the conveyance drive circuit 51 generates a drive signal based on the input control signal and outputs it to the conveyance motor 26. The conveyance motor 26 is driven based on the input drive signal to operate the conveyance device 22 and convey the recording medium A in the forward and backward directions relative to the ejection head 10.

[0032] The control device 40 is connected to the movement motor 29 via a movement drive circuit 52. The control device 40 outputs a control signal to the movement drive circuit 52, and the movement drive circuit 52 generates a drive signal based on the input control signal and outputs it to the movement motor 29. The movement motor 29 is driven based on the input drive signal to operate the movement device 23, and moves the carriage 27 carrying the ejection head 10 in the left-right direction.

[0033] The display device 53 is, for example, a liquid crystal display, and displays images printed by the liquid ejection device 1 and various types of information under the control of the control device 40. The input device 54 is, for example, a button switch, a touch panel integrated with the display device 53, or the like. The input device 54 allows a user to input various types of information (instructions for executing operations, setting values, etc.) to the control device 40 through input operations.

[0034] The temperature sensor 55 is a thermometer or the like that detects information related to the temperatures around the first ejection head 10A and the second ejection head 10B. The temperature sensor 55 may be configured to directly detect the temperature of the liquid inside each ejection head 10, or may be configured to indirectly detect the temperature of the internal liquid from the outer surface of each ejection head 10 or its vicinity. Furthermore, the temperature sensor 55 is not limited to a configuration that detects the temperature itself, and may be configured to detect other parameters that have a correlation with temperature (for example, the viscosity of the liquid) and estimate the temperature through calculation by the control device 40.

[0035] The humidity sensor 56 is a thermometer or the like that detects information related to the temperatures around the first ejection head 10A and the second ejection head 10B. The humidity sender 56 is preferably configured to directly detect the humidity near the nozzles 14 of each ejection head 10, but is not limited to this. The humidity sender 56 may be configured to indirectly detect the humidity near the nozzles 14, or to detect another parameter that has a correlation with humidity and estimate the humidity through calculation by the control device 40.

[0036] The imaging device 57 is a device that captures an image of an image printed on the recording medium A by the liquid ejected from the ejection head 10 within the housing 2 of the liquid ejection device 1. A digital camera or scanner equipped with an image sensor such as a CMOS or CCD can be used as the imaging device 57. The imaging device 57 inputs imaging data obtained by reading the image on the recording medium A to the control device 40.

[0037] <Basic operations of printing process> In such a liquid ejection device 1, for example, when the control device 40 receives a print job from the external device 60, the liquid ejection device 1 prints an image on the recording medium A based on the print job. For example, the control device 40 executes a printing process (path printing process) that executes a discharge operation in which the ejection head 10 is moved in the left-right direction by the movement device 23 while discharging liquid from the nozzles 14, and a transport operation in which the transport device 22 transports the recording medium A in the front-rear direction.

[0038] Here, the liquid ejection device 1 according to this embodiment has two ejection heads 10 that eject the same type of liquid, offset in the front-to-rear direction, which is essentially the same as having a longer ejection head in the front-to-rear direction, and this can achieve faster printing processing. However, with this configuration, high precision is required for the fixed positions of the two ejection heads 10 to the carriage 27, and if they are misaligned from their designed positions, unintended streaks (banding) may occur in the printed image, which could result in a deterioration in image quality.

[0039] To address this banding, the liquid ejection device 1 provides the seam regions 11c to 13c described in Fig. 2 between the first ejection head 10A and the second ejection head 10B. In the seam regions, masks are set so that only some of the nozzles 14 of each of the first ejection head 10A and the second ejection head 10B are permitted to be used for ejecting liquid during the printing process. In other words, shingled printing is performed by the first ejection head 10A and the second ejection head 10B using the masks in the seam regions.

[0040] <Normal mask> The masks will be described below. Information about the masks is stored in the storage unit 42 of the control device 40. FIG. 4A is a schematic diagram for explaining a mask (normal mask) used to prevent banding, and illustrates a normal mask set on the nozzles 14 in the spot color seam region 12c provided for the first spot color head 12a and the second spot color head 12b. However, similar normal masks may also be set in the other color seam regions 11c and the white background seam region 13c. The same applies to the other masks (special masks A, B, and C) described below.

[0041] Note that the left side of Fig. 4A illustrates an image of the arrangement of the first spot color head 12a and the second spot color head 12b. Also, the center of Fig. 4A shows a graph showing the usage permission rate (0 to 100%) of the nozzle 14 at each position in the front-to-rear direction, with the vertical axis representing the position of the nozzle 14 in the front-to-rear direction and the horizontal axis representing the usage permission rate. Also, in this graph, the upper solid line corresponds to the first spot color head 12a, and the lower dashed line corresponds to the second spot color head 12b.

[0042] Furthermore, the right side of FIG. 4A shows an image of a mask set in the spot color seam region 12c, where one rectangle X represents one nozzle 14, the hatched rectangle X1 represents a nozzle 14 that is permitted to be used, and the open rectangle X2 represents a nozzle 14 that is not permitted to be used. In this image, the upper diagram shows a first mask for the nozzles 14 located in the spot color seam region 12c of the first spot color head 12a, and the lower diagram shows a second mask for the nozzles 14 located in the seam region 12c of the second spot color head 12b. A set of these first and second masks forms the mask for the spot color seam region 12c. In this example, the first spot color head 12a includes the first six nozzles 14a from the front end to the rear in the spot color seam region 12c, and the second spot color head 12b includes the first six nozzles 14b from the rear end to the front in the spot color seam region 12c.

[0043] Note that Figures 4B, 5A, and 5B, which will be described later, are schematic diagrams explaining other masks, and similar to Figure 4A, show an arrangement image on the left, a graph related to the permission rate of use in the center, and an image of the mask on the right.

[0044] 4A, in this normal mask, among the first nozzles 14a located in the spot color seam region 12c, the number of first nozzles 14a aligned in the left-right direction that are used (permitted to be used) for ejecting liquid increases at a predetermined rate R1 toward the rear. In other words, for the first nozzles 14a located in the spot color seam region 12c, the rate of permission to use for one nozzle row 17 increases at rate R1 toward the rear of the nozzle row 17.

[0045] Furthermore, among the second nozzles 14b located in the spot color seam region 12c, the number of nozzles that are used (permitted to be used) for ejecting liquid among the multiple second nozzles 14b aligned in the left-right direction decreases toward the rear at a predetermined rate R1. In other words, for the second nozzles 14b located in the spot color seam region 12c, the rate at which permission to use for one nozzle row 17 decreases at rate R1 toward the rear of the nozzle row 17.

[0046] As described above, the rate R1 at which the use permission rate increases in the first mask corresponding to the first nozzle 14a and the rate R1 at which the use permission rate decreases in the second mask corresponding to the second nozzle 14b are set to be the same. When the first mask and the second mask are overlapped, the use permission rate of the nozzles 14 at each position in the front-to-rear direction is set to 100%.

[0047] By using such a mask, the occurrence of the above-mentioned banding can be suppressed. On the other hand, when such a mask is used, some nozzles 14 are used less frequently, and the ink inside those nozzles 14 is more likely to dry out. For example, in the case of the normal mask shown in FIG. 4A, the nozzles 14a closer to the front end of the first spot color head 12a are more likely to dry out, and the nozzles 14b closer to the rear end of the second spot color head 12b are more likely to dry out. Furthermore, in general, in printing processes, spot color inks tend to be used less frequently than process color inks. Therefore, the nozzles 14 for which a mask is set in the spot color head 12 are particularly prone to drying out.

[0048] Therefore, the liquid ejection device 1 according to this embodiment is provided with a plurality of masks with different recovery powers that can recover the dried ink in the nozzle 14 (stored in the memory unit 42), and is configured to select and use one of the plurality of masks depending on the risk of drying.

[0049] A further explanation of the "permission" of nozzle use described above is provided. For example, if one ejection head 10 has 210 nozzles 14, each nozzle 14 is assigned an identification number, which is stored in the memory unit 42 or the like. A flag indicating permission for use or a flag indicating unusable is assigned to each identification number, and the relationship between the identification number and the set flag is managed by table data. For example, if flags are represented by two numbers, "0" and "1," a permission for use flag is represented by "0," and an unusable flag is represented by "1." The "permission" of nozzle use means that drive signals are input only to the drive elements 16 of some or all of the nozzles selected according to the print image among the nozzles with identification numbers for which a permission for use flag is set, or that drive signals are not input to the corresponding drive elements 16 of nozzles with identification numbers for which a unusable flag is set.

[0050] <Special Mask A> FIG. 4B is a schematic diagram for explaining another mask (special mask A). In the first mask of this special mask A, among the plurality of first nozzles 14a arranged in the left-right direction in the characteristic joint region 12c, the number of nozzles used (permitted to be used) for liquid ejection increases at a predetermined ratio R2 toward the rear. In other words, in the case of the first nozzles 14a located in the characteristic joint region 12c, the permission rate for one nozzle row 17 increases at the ratio R2 as the rear nozzle row 17 is reached.

[0051] Also, in the second mask, among the plurality of second nozzles 14b arranged in the left-right direction in the characteristic joint region 12c, the number of nozzles used (permitted to be used) for liquid ejection decreases at a predetermined ratio R2 toward the rear. In other words, in the case of the second nozzles 14b located in the characteristic joint region 12c, the permission rate for one nozzle row 17 decreases at the ratio R2 as the rear nozzle row 17 is reached.

[0052] Note that the ratio R2 in the special mask A is smaller than the ratio R1 in the normal mask (0 < R2 < R1). Therefore, as can be seen by comparing the normal mask of FIG. 4A and the special mask A of FIG. 4B, in the case of the normal mask, the permission rate changes greatly in the front-rear direction, but the change mode of the permission rate in the special mask A is smaller than that of the normal mask. Also, for the special mask A, when the first mask and the second mask are overlapped, the permission rate of the nozzles 14 at each position in the front-rear direction is set to 100%.

[0053] Such a special mask A has a higher permission rate for the nozzles 14a closer to the front end of the first characteristic head 12a and the nozzles 14b closer to the rear end of the second characteristic head 12b than the normal mask. Therefore, by using the special mask A instead of the normal mask as the mask used in the characteristic joint region 12c, the drying of the ink in each of the nozzles 14a, 14b can be restored.

[0054] <Special mask B> FIG. 5A is a schematic diagram for explaining another mask (special mask B). In the first mask of this special mask B, among the plurality of first nozzles 14a arranged in the left-right direction in the feature connection area 12c, the number of nozzles used (permitted to be used) for liquid ejection increases at a predetermined ratio R3 toward the rear. More precisely, in the example of FIG. 5A, the ratio R3 = 0, and the usage permission rate is a constant value (50%) regardless of the position of the first nozzle 14a.

[0055] Also, in the second mask, among the plurality of second nozzles 14b arranged in the left-right direction in the feature connection area 12c, the number of nozzles used (permitted to be used) for liquid ejection decreases at a predetermined ratio R3 toward the rear. More precisely, in the example of FIG. 5A, the ratio R3 = 0, and the usage permission rate is a constant value (50%) regardless of the position of the first nozzle 14a.

[0056] Thus, the ratio R3 in the special mask B is even smaller than the ratio R2 in the special mask A (R3 < R2). Therefore, as can be seen by comparing the special mask A in FIG. 4B with the special mask B in FIG. 5A, in the case of the special mask A, the usage permission rate changes in the front-rear direction, but the change pattern of the usage permission rate in the special mask B is even smaller than that in the special mask A and hardly changes. Note that for the special mask B as well, when the first mask and the second mask are overlapped, the usage permission rate of the nozzles 14 at each position in the front-rear direction is set to 100%.

[0057] Such a special mask B has a higher usage permission rate for the nozzles 14a closer to the front end of the first feature head 12a and the nozzles 14b closer to the rear end of the second feature head 12b than the special mask A. Therefore, by using the special mask B instead of the normal mask or the special mask A as the mask used in the feature connection area 12c, the drying of the ink in each of the nozzles 14a, 14b can be more powerfully restored.

[0058] The normal mask, special mask A, and special mask B described above have different banding suppression effects (anti-banding level) and recovery effects (anti-drying level) for the liquid due to differences in the manner in which the usage permission rate of the nozzles 14 changes. Specifically, the anti-banding level decreases in the order of the normal mask, special mask A, and special mask B. On the other hand, the anti-drying level increases in the order of the normal mask, special mask A, and special mask B. The liquid ejection device 1 then selects one of the masks depending on the risk of drying.

[0059] <Special Mask C> The liquid ejection device 1 has yet another mask (special mask C) selected from a perspective other than the risk of drying, which will now be described. FIG. 5B is a schematic diagram illustrating special mask C. The first mask of this special mask C prohibits use of all corresponding nozzles 14a, while the second mask permits use of all corresponding nozzles 14b. In other words, this special mask C is a mask that does not use the nozzles 14a of the first special color head 12a in the special color seam region 12c, but only uses the nozzles 14b of the second special color head 12b.

[0060] Such a special mask C is selected when a non-discharge occurs in the first nozzle 14a in the spot color seam region 12c. Note that a special mask C that uses only the nozzles 14a of the first spot color head 12a and does not use the nozzles 14b of the second spot color head 12b in the spot color seam region 12c, which is the opposite of the example shown in Fig. 5B, is also stored in the storage unit 42. Such a special mask C is selected when a non-discharge occurs in the second nozzle 14b in the spot color seam region 12c.

[0061] <Printing process> Next, the printing process performed by the liquid ejection device 1 described above will be described. FIG. 6 is a flowchart showing an example of the operation of the liquid ejection device 1 in the printing process. The liquid ejection device 1 essentially starts the printing process by receiving a print job. This printing process is a process of printing using a selected mask based on the print job, and is started by receiving the print job. That is, the liquid ejection device 1 determines whether or not a print job has been received (step S1), and if it determines that the print job has not been received (S1: NO), it repeats the operation of step S1, and if it determines that the print job has been received (S1: YES), it proceeds to the next step and performs a flushing process (step S2).

[0062] In the flushing process (S2), the liquid ejection device 1 moves the carriage 27 to a maintenance area outside the platen 20, where liquid is ejected (discharged) from the nozzles 14 (first nozzles 14a and second nozzles 14b) of each ejection head 10. This causes the nozzles 14 of each ejection head 10 to go from a dry state to a refreshed state.

[0063] Next, the liquid ejection device 1 determines whether or not there is a non-ejecting nozzle (Step S3). More specifically, a non-ejecting detection process is executed to detect whether or not there is a non-ejecting nozzle among the first nozzles 14a and the second nozzles 14b included in the seam region.

[0064] If it is determined that there are no non-ejecting nozzles (S3: YES) as a result of the determination of the presence or absence of non-ejecting nozzles, the control device 40 sets the use of a normal mask for the seam region as an example of a mask selection process (step S4-1). An example of this normal mask is the configuration shown in Fig. 4A. Note that, rather than setting the normal mask when there are no non-ejecting nozzles, the use of the normal mask may be set as the initial setting in the printing process, and the mask setting may be performed only when a mask other than the normal mask is to be used.

[0065] On the other hand, if the result of the determination of the presence or absence of non-ejecting nozzles indicates that there are non-ejecting nozzles (S3: NO), the control device 40 selects the use of special mask C for the seam region (step S4-2) as an example of a mask selection process. For example, if it is determined that some or all of the first nozzles 14a of the two spot color heads 12a and 12b are non-ejecting in the spot color seam region 12c, a special mask C is selected for the spot color seam region 12c, which does not use any of the first nozzles 14a in the spot color seam region 12c and uses only the second nozzles 14b. An example of such a special mask C is the configuration shown in FIG. 5B. Note that the selection and setting of the normal mask or special mask C is performed before the start of the print job (S5). In other words, switching from the normal mask to the special mask C during printing, for example, may result in unexpected degradation of image quality, but switching before the start of the print job can avoid such degradation of image quality.

[0066] The determination of the presence or absence of a non-ejecting nozzle may be made by any known determination method, and is not particularly limited. For example, a method may be used in which a light-emitting element and a light-receiving element are arranged on either side of the flight path of the liquid ejected from the nozzle 14, and light is emitted, and the presence or absence of liquid ejection is determined based on a change in the amount of light received when the drive element 16 is driven. Alternatively, a method may be used in which a predetermined voltage is applied between the ejection head 10 and a counter electrode arranged below it, and the presence or absence of liquid ejection is determined based on a change in voltage when the drive element 16 is driven to eject liquid (charged liquid) from the nozzle 14. Note that this determination of the presence or absence of a non-ejecting nozzle (S3) may be performed simultaneously with the flushing process (S2).

[0067] If the normal mask is set in step S4-1 or the special mask C is set in step S4-2, the liquid ejection device 1 starts a print job (step S5). That is, printing is performed using the mask selected in step S4-1 or S4-2 based on the print job. For example, when the liquid ejection device 1 starts a print job, it starts a page printing process (step S6) and then a pass printing process (step S7). Here, the page printing process (S6) is a process for managing the printing operation for each page when the print job involves printing one or more pages of images. Furthermore, the pass printing process (S7) is a process for managing the printing operation for each pass when the image to be printed on one page is composed of one or more passes, and the selected mask is used in the printing operation. Therefore, in a print job, printing is performed in pass units, which are the smallest unit. Once printing of all passes included in one page has been completed, printing of the next page is performed pass by pass. Then, when printing of all pages has been completed, the print job ends.

[0068] After starting pass printing (S7), the liquid ejection device 1 determines whether pass printing has ended (step S8). If it determines that pass printing has not ended (S8: NO), the process of step S8 is repeated, and if it determines that pass printing has ended (S8: YES), it determines whether flushing processing should be performed (step S9). In step S9, it is determined that flushing processing should be performed if a predetermined condition is met. An example of the predetermined condition is a state in which the dryness level of the liquid in the nozzles 14 has reached a predetermined level or more. For example, the predetermined condition may be a state in which a predetermined period of time has passed since the previous flushing processing.

[0069] If it is determined in step S9 that the flushing process is to be performed (S9: YES), the flushing process is performed (step S10). If it is determined that the flushing process is not to be performed (S9: NO), or if the flushing process is performed in step S10, a mask setting process is performed (step S11). The mask setting process (S11) will be described later.

[0070] After completing the mask setting process in step S11 to set the mask to be used in the seam region, the liquid ejection device 1 next determines whether or not the pass printing process has been completed for all passes in the current page (step S12). If it determines that not all passes have been completed (S12: NO), the process returns to step S7 and starts the pass printing process for the next pass. If it determines that all passes have been completed (S12: YES), the process determines whether or not the page printing process has been completed for all pages in the current print job (step S13). If it determines that not all pages have been completed (S13: NO), the process returns to step S6 and starts the page printing process for the next page.

[0071] If it is determined that all pages have been completed (S13: YES), it is then determined whether all received print jobs have been completed (step S14). For example, if another print job is received while one print job is being executed, there is an unexecuted print job, so in that case it is determined in step S14 that all print jobs have not been completed (S14: NO), and processing is carried out from step S5 to execute the next print job. On the other hand, if there is no such unexecuted print job (S14: NO), the printing process of FIG. 6 is terminated.

[0072] <Mask setting process> The mask setting process executed in step S11 will now be described in detail. The mask setting process includes a risk acquisition process and a mask selection process. The risk acquisition process is a process for acquiring information regarding the drying risk of the liquid in each of the first nozzle 14a and the second nozzle 14b included in the seam region. The drying risk can be, for example, the elapsed time since the previous flushing process. The mask selection process is a process for selecting one mask from among multiple masks with different rates of change in usage permission rate, depending on the drying risk.

[0073] As described above, the mask determines the rate at which the permission rate for one nozzle row 17 of the first nozzles 14a included in the joint region increases toward the rear, and the rate at which the permission rate for one nozzle row 17 of the second nozzles 14b included in the joint region decreases toward the rear. A plurality of types of masks, such as the normal mask (ratio: R1) in FIG. A4, the special mask B (ratio: R2) in FIG. 4B, and the special mask B (ratio: R3) in FIG. 5A, are prepared in advance and stored in the storage unit 42.

[0074] FIG. 7 is a flowchart showing an example of mask setting processing, and corresponds to the content of the subroutine of step S11 in the flowchart of FIG. 6. As shown in FIG. 7, in the mask setting processing, the liquid discharge device 1 first checks the type of the current mask (step S20). Then, it is determined whether the current mask is a normal mask (step S21). If it is determined that the current mask is a normal mask (S21: YES), it is determined whether the first period has elapsed since the previous flushing process (step S22). That is, in this step S22, as an example of risk acquisition processing, the elapsed time since the previous flushing process is acquired, and it is determined whether the acquired elapsed time has elapsed the first period.

[0075] If it is determined in step S22 that the first period has elapsed (S22: YES), the special mask A is selected (step S23). That is, if the first period has elapsed since the previous flushing process, it can be determined that the liquid in the nozzle 14 is somewhat dry and the drying risk is high. Therefore, the liquid discharge device 1 selects to switch from the current normal mask (ratio: R1) to the special mask A (ratios: R2, R2 < R1) with a drying level one higher.

[0076] If it is determined in step S22 that the first period has not elapsed (S22: NO), then it is further determined whether the printing period has elapsed the second period (step S24). That is, in this step S24, as an example of the risk acquisition process, the printing period with the normal mask is acquired, and it is determined whether the acquired printing period has elapsed the second period.

[0077] If it is determined in step S24 that the second period has elapsed (S24: YES), then the special mask A is selected (S23). That is, even if the first period has not elapsed since the previous flushing process (S22: NO), if the printing period with the normal mask having a low drying level has elapsed the second period (S24: YES), it can be determined that the liquid in the nozzle 14 is in a dry state and the drying risk is high. Therefore, the liquid ejection device 1 selects to switch from the current normal mask (ratio: R1) to the special mask A (ratio: R2, R2 < R1) having a drying level one level higher.

[0078] If it is determined in step S24 that the second period has not elapsed (S24: NO), then the normal mask is selected (step S25). That is, if the first period has not elapsed since the previous flushing process (S22: NO) and the printing period with the normal mask has not elapsed the second period (S24: NO), it can be determined that the drying of the liquid in the nozzle has not progressed much and the drying risk is low. Therefore, the liquid ejection device 1 selects to maintain the current normal mask and takes banding countermeasures.

[0079] On the other hand, if it is determined in step S21 that the current mask is not the normal mask (S21: NO), then next, it is determined whether the current mask is the special mask A or the special mask B (step S26). Here, if it is determined that it is neither the special mask A nor the special mask B (S26: NO), it means that the current mask is the special mask C when there is a non-ejecting nozzle. Therefore, in this case, it is determined not to change the mask from the special mask C (step S27).

[0080] If it is determined in step S26 that the mask is special mask A or special mask B (S26: YES), it is determined whether a first period has elapsed since the previous flushing process (step S28). That is, in step S28, the time elapsed since the previous flushing process is obtained as an example of risk acquisition processing, and it is determined whether the obtained elapsed time has elapsed the first period.

[0081] If it is determined in step S28 that the first period has not elapsed (S28: NO), the normal mask is selected (step S29). In other words, if the first period has not elapsed since the previous flushing process, it can be determined that the liquid in the nozzles 14 has not yet dried and the risk of drying is low. Therefore, the liquid ejection device 1 selects to switch from the current special mask A or special mask B to a normal mask which has a low dryness resistance level but a high banding resistance level.

[0082] If it is determined in step S28 that the first period has elapsed (S28: YES), it is further determined whether the printing period has elapsed the second period (step S30). That is, in step S30, the printing period using special mask A or special mask B is acquired as an example of risk acquisition processing, and it is determined whether the acquired printing period has elapsed the second period.

[0083] If it is determined in step S30 that the second period has elapsed (S30: YES), the normal mask is selected (S29). That is, even if the first period has elapsed since the previous flushing process (S28: YES), if the printing period using special mask A or special mask B, which has a high dryness resistance level, has elapsed the second period (S30: YES), it can be determined that the liquid in the nozzles 14 has not dried very much and the risk of drying is low. Therefore, the liquid ejection device 1 selects to switch from the current special mask A or special mask B to a normal mask, which has a low dryness resistance level but a high banding resistance level.

[0084] If it is determined in step S30 that the second period has not elapsed (S30: NO), the liquid ejection device 1 selects not to change from the current mask (step S31). In other words, if the first period has elapsed since the previous flushing process (S28: YES) and the printing period using special mask A or special mask B has not elapsed the second period (S30: NO), it can be determined that the liquid in the nozzles 14 has not recovered from drying and that the risk of drying is high. Therefore, the liquid ejection device 1 selects to maintain the current special mask A or special mask B and takes measures to prevent drying.

[0085] The processes in steps S23, S25, S27, S29, and S31 correspond to a mask selection process for selecting one mask depending on the risk of dryness. After the mask selection process is completed, the subroutine for the mask setting process in step S11 ends. After that, the process proceeds to step S12 in the flowchart of FIG. 6.

[0086] Here, the mask setting process, including this mask selection process, is performed before or after the start of pass printing process for one pass during execution of a print job. For example, as shown in Figure 6, the mask setting process (S11) is performed after the previous pass printing process is completed or before the next pass printing process is started. In this way, the mask is not switched during the pass printing process, thereby avoiding degradation of image quality due to mask switching.

[0087] 7 (particularly the process in S23) is configured to select a mask with a smaller rate of change in the usage permission rate as the risk of drying increases. As a result, the higher the risk of drying, the more frequently the nozzles 14 that are used less frequently can be used, allowing the ink in the nozzles 14 to recover from drying. Note that the "first periods" in steps S22 and S28 may be different periods, and the "second periods" in steps S24 and S30 may also be different periods. Furthermore, the first period in step S28 or the second period in step S30 may be different depending on whether the current mask is special mask A or special mask B.

[0088] <Variation 1> Fig. 8 is a flowchart showing another example of the mask setting process, which corresponds to the contents of the subroutine of step S11 in the flowchart of Fig. 6. Note that, although the mask setting process will be described here with a focus on measures to prevent the drying of spot color ink, similar processes can also be applied to measures to prevent the drying of other types of liquid (color inks and white inks).

[0089] The mask setting process shown in Figure 8 includes a risk acquisition process that acquires the amount of spot color ink used in the next pass as information related to the risk of drying, and a mask selection process that selects a mask based on the acquired ink usage amount. The amount of spot color ink used can be acquired from information included in the print job received by the liquid ejection device 1. Furthermore, in this mask selection process, if the amount of spot color ink ejected in the next pass is equal to or greater than a predetermined first threshold, a mask with a smaller percentage related to the change in usage permission rate is selected than when the amount is less than the first threshold. Furthermore, in this mask process, if the amount of spot color ink ejected in the next pass is less than a predetermined second threshold (<first threshold), a mask with a smaller percentage related to the change in usage permission rate is selected than when the amount is equal to or greater than the second threshold.

[0090] A more detailed explanation follows. As shown in Fig. 8, in the mask setting process, the liquid ejection device 1 determines whether the usage amount (ejection amount) of the spot color ink in the next pass is equal to or greater than a predetermined first threshold (step S40). If it is determined that the usage amount is equal to or greater than the first threshold (S40: YES), special mask B is selected (step S41). In other words, if the usage amount of the spot color ink in the next pass is relatively large (S40: YES), this can be seen as an opportunity to recover the ink in the nozzles 14 of the spot color head 12 from drying. Therefore, by selecting special mask B (ratio: R3), which has the highest dryness level (S41), the ink in the nozzles 14 can be effectively recovered from drying in the next pass printing process.

[0091] On the other hand, if it is determined that the amount is less than the first threshold (S40: NO), it is further determined whether the amount of spot color ink used (ejection amount) in the next pass is less than a predetermined second threshold (<first threshold) (step S42).If it is determined that the amount is less than the second threshold (S42: YES), special mask A is selected (step S43), and if it is determined that the amount is equal to or greater than the second threshold (S42: NO), the normal mask is selected (step S44).

[0092] That is, if the amount of spot color ink used in the next pass is relatively small (S42: YES), there is a possibility that the ink in the nozzles 14 of the spot color head 12 will dry out due to the next pass printing process. Therefore, by selecting special mask A, which has a relatively high level of resistance to drying (S43), it is possible to suppress the drying of ink in the next pass printing process. Also, if the amount of spot color ink used in the next pass is neither particularly large nor particularly small (S42: NO), it is possible to take measures against banding by selecting the normal mask (S44).

[0093] <Variation 2> Fig. 9 is a flowchart showing another example of the mask setting process, and shows three processes (steps S50, S51, and S52) added between step S2 and step S3 in the flowchart of Fig. 6. In the example of Fig. 9, when a print job includes a print process in the spot color seam region 12c, a mask with a smaller percentage related to the change in the usage permission rate is selected in the mask selection process than when a print job does not include a print process in the spot color seam region 12c.

[0094] Specifically, in the case of Figure 9, after flushing processing (S2) is performed, it is determined based on the content of the print job whether spot color ink will be used in the print job to be executed (step S50). Because spot color ink is generally used infrequently, information regarding the use of spot color ink corresponds to information regarding the risk of drying. Therefore, the operation of obtaining information regarding whether spot color ink will be used from the print job corresponds to risk obtaining processing.

[0095] Next, when it is determined in step S50 that the special ink is used (S50: YES), the special mask A (ratio: R2, R2 < R1) is selected (step S51), and when it is determined that the special ink is not used (S50: NO), the normal mask (ratio: R1) is selected (step S52). The operations in steps S51 and S52 such as this correspond to the mask selection process of selecting a mask according to the drying risk.

[0096] By executing such operations, the liquid discharge device 1 can suppress the drying of the special ink by using a mask with a high drying level in a printing job using the special ink. When adopting the operation shown in FIG. 9, the mask selected by the subsequent processes of steps S3, S4-1, and S4-2 may overwrite the mask selected in steps S51 and S52. Also, when adopting the operation shown in FIG. 9, the mask setting process in step S11 may be omitted.

[0097] <Modified Example 3> FIG. 10 is a flowchart showing another example of the mask setting process, and corresponds to the content of the subroutine of step S11 in the flowchart of FIG. 6. The processes of steps S60 to S64 shown in FIG. 10 are performed immediately after the start of the mask setting process in FIG. 7, that is, before the execution of step S20.

[0098] Also, in the example of FIG. 10, in the mask selection process, even if other drying risks are the same, when the temperature detected by the temperature sensor 55 is equal to or higher than a predetermined threshold temperature, a mask with a smaller ratio regarding the change in the use permission rate is selected than when it is lower than the threshold temperature. Also, in the example of FIG. 10, in the mask selection process, even if other drying risks are the same, when the humidity detected by the humidity sensor 56 is less than a predetermined threshold humidity, a mask with a smaller ratio regarding the change in the use permission rate is selected than when it is equal to or higher than the threshold humidity.

[0099] Specifically, in the case of FIG. 10, at the beginning of the mask setting process, the temperature and humidity are detected (step S60). The temperature and humidity correspond to information regarding the risk of the liquid in the nozzle 14 drying out. Therefore, detecting the temperature and humidity corresponds to the risk acquisition process. Next, the liquid ejection device 1 determines whether the temperature is equal to or higher than a predetermined threshold temperature (step S61). If it is determined that the temperature is equal to or higher than the threshold temperature (S61: YES), the first period described in FIG. 7 is set to a relatively short period (e.g., 30 seconds), and the second period is also set to a relatively short period (e.g., 10 seconds) (step S62).

[0100] On the other hand, if it is determined in step S61 that the temperature is below the predetermined threshold temperature (S61: NO), it is further determined whether the humidity is equal to or greater than the predetermined threshold humidity (step S63). If it is determined that the humidity is below the threshold humidity (S63: NO), the above-mentioned step S62 is executed, and if it is determined that the humidity is equal to or greater than the threshold humidity (S63: YES), the first period is set to a relatively long period (for example, 45 seconds), and the second period is also set to a relatively long period (for example, 15 seconds) (step S64).

[0101] By performing the above-described operations, the liquid ejection device 1 is more likely to select a mask with a smaller percentage change in the usable rate (i.e., a mask with a high level of resistance to dryness) when the temperature is relatively high and the mask is prone to dryness than when the temperature is relatively low. Similarly, when the humidity is relatively low and the mask is prone to dryness, the liquid ejection device 1 is more likely to select a mask with a smaller percentage change in the usable rate (i.e., a mask with a high level of resistance to dryness) than when the humidity is relatively high. Therefore, the liquid ejection device 1 can select an appropriate mask based on the risk of dryness caused by temperature and humidity.

[0102] <Variation 4> Figures 11A and 11B are flowcharts showing another example of the mask setting process, and correspond to the contents of the subroutine of step S11 in the flowchart of Figure 6. Note that the processes of steps S70 to S76 shown in Figure 11A replace the processes of steps S22 to S25 after step S21 in Figure 7. Furthermore, the processes of steps S80 to S86 shown in Figure 11B replace the processes of steps S28 to S31 after step S26 in Figure 7.

[0103] 11A and 11B, when the proportion of small droplets among the small and large droplets ejected in the seam area during printing is equal to or greater than a predetermined threshold (small droplet rate), a mask with a smaller percentage change in the usage permission rate is selected than when the proportion is less than the threshold. In other words, large droplets, which have a larger volume of liquid ejected from the nozzles 14, are less likely to dry and are easier to recover from a dried state than small droplets, which have a smaller volume. Therefore, when the small droplet rate is low, drying is less likely to progress, and when the small droplet rate is high, drying is more likely to progress. Therefore, a mask is selected based on this risk of drying. The volume of liquid ejected from the nozzles 14 can be changed by adjusting the amplitude or wavelength of the voltage consisting of the pulse waveform applied to the drive elements 16, allowing large droplets and small droplets to be selectively ejected.

[0104] Specifically, in the case of FIG. 11A, if the current mask is the normal mask (S21: YES), it is determined whether a first period has elapsed since the previous flushing process (step S70). If it is determined that the first period has not elapsed (S70: NO), it is determined whether the small droplet rate is less than a predetermined threshold value (e.g., 80%) (step S71). If it is determined that the small droplet rate is less than the threshold value (S71: YES), the mask is not changed and the normal mask is maintained (step S72). On the other hand, if it is determined that the small droplet rate is equal to or greater than the threshold value (S71: NO), special mask A is selected (step S74).

[0105] Furthermore, if it is determined in step S70 that the first period has elapsed (S70: YES), it is determined whether the printing period using the current normal mask has elapsed a predetermined third period (step S73). If it is determined that the third period has elapsed (S73: YES), special mask A is selected (S74). On the other hand, if it is determined that the third period has not elapsed (S73: NO), it is determined whether the small droplet rate is less than a predetermined threshold value (e.g., 80%) (step S75). If it is determined that the small droplet rate is equal to or greater than the threshold value (S75: NO), special mask A is selected (S74). If it is determined that the small droplet rate is less than the threshold value (S75: YES), the mask is not changed and the normal mask is maintained (step S76).

[0106] In the case of FIG. 11B, if the current mask is special mask A or special mask B (S26: YES), it is determined whether a first period has elapsed since the previous flushing process (step S80). If it is determined that the first period has not elapsed (S80: NO), it is determined whether the small droplet rate is less than a predetermined threshold value (e.g., 80%) (step S81). If it is determined that the small droplet rate is less than the threshold value (S81: YES), the mask is changed and the normal mask is selected (step S82). On the other hand, if it is determined that the small droplet rate is equal to or greater than the threshold value (S81: NO), the mask is not changed and special mask A or special mask B is maintained (step S84).

[0107] If it is determined in step S80 that the first period has elapsed (S80: YES), it is then determined whether the printing period using the current special mask A or special mask B has elapsed a predetermined third period (step S83). If it is determined that the third period has not elapsed (S83: NO), the mask is not changed and special mask A or special mask B is maintained (S84). On the other hand, if it is determined that the third period has elapsed (S83: YES), it is determined whether the small droplet rate is less than a predetermined threshold (e.g., 80%) (step S85). If it is determined that the small droplet rate is equal to or greater than the threshold (S85: NO), the mask is not changed and special mask A or special mask B is maintained (S84). If it is determined that the small droplet rate is less than the threshold (S85: YES), the mask is changed and the normal mask is selected (step S86).

[0108] By performing the above-described operations, the liquid ejection device 1 can select a mask suitable for preventing drying, depending on the droplet rate, which is an example of the risk of drying.

[0109] <Variation 5> Fig. 12 is a flowchart showing another example of the mask setting process. Note that the processes of steps S90 to S93 shown in Fig. 12 are executed after a mask is selected in the mask setting process. These processes are intended to select a mask that has a larger proportion of change in the usage permission rate when the degree of banding detected in the seam region in the liquid ejection device 1 is high than when the degree of banding is low. Note that the selection of a mask in the mask setting process may correspond to, for example, the processes of steps S23, S27, S29, and S31 in Fig. 7, the processes of steps S41, S43, and S44 in Fig. 8, the processes of steps S72, S74, and S76 in Fig. 11A, and the processes of steps S82, S84, and S86 in Fig. 11B.

[0110] 12, once a mask is selected, banding detection is performed on the seam region (step S90). That is, a banding detection process is executed to detect banding in the printed image caused by a deviation in the relative position of the first ejection head 10A and the second ejection head 10B. This banding detection process can be performed, for example, by capturing an image of the image printed by the first ejection head 10A and the second ejection head 10B using the imaging device 57 provided in the liquid ejection device 1, and then analyzing the captured data using the control device 40.

[0111] The banding detection process also involves acquiring (calculating) the level (degree) of banding from the captured image data. The level of banding can be determined, for example, by extracting points from the captured image data where the difference in image contrast is equal to or greater than a predetermined value, and judging from the length of succession of such points. Note that the method for determining the level of banding is not limited to this, and other methods may also be used.

[0112] The liquid ejection device 1 determines whether the banding level detected in step S90 is equal to or greater than a predetermined threshold (step S91). If it is determined that the banding level is equal to or greater than the threshold (S91), the dryness level of the mask is lowered by one (step S92). That is, the previously selected mask is switched to a mask with a dryness level lowered by one level. On the other hand, if it is determined in step S91 that the banding level is less than the threshold (S91: NO), the mask is not changed (step S93).

[0113] By performing this operation, the liquid ejection device 1 selects a mask with a larger percentage of change in the usable permission rate when the degree of banding detected from the printed image in the seam area is large than when the degree of banding is small. This prevents the degradation of image quality due to banding from becoming more noticeable when a mask with a high drying resistance level is selected when banding occurs.

[0114] 13A to 13C are schematic diagrams illustrating the type of mask and the degree to which banding is noticeable when banding exists in a seam region due to a misalignment of the distance Δ between the first discharge head 10A and the second discharge head 10B in the front-to-rear direction. FIG. 13A shows the case when a normal mask is used, FIG. 13B shows the case when special mask A is used, and FIG. 13C shows the case when special mask B is used. Note that the normal mask has a "low" dryness resistance level and a "high" banding resistance level. Special mask A has a "medium" dryness resistance level and a "medium" banding resistance level. Special mask B has a "high" dryness resistance level and a "low" banding resistance level.

[0115] The left side of each figure shows an image of the arrangement of the first spot color head 12a and the second spot color head 12b. The center of each figure shows a graph indicating the usage permission rate (0 to 100%) of the nozzles 14 at each position in the front-to-rear direction, with the vertical axis representing the position of the nozzles 14 in the front-to-rear direction and the horizontal axis representing the usage permission rate. In this graph, the upper solid line corresponds to the first spot color head 12a, and the lower dashed line corresponds to the second spot color head 12b. The right side of each figure shows a graph indicating the total value of the usage permission rate of the nozzles 14 at each position in the front-to-rear direction for the first spot color head 12a and the second spot color head 12b.

[0116] In the case of the normal mask shown in Figure 13A, the dryness resistance level is low but the banding resistance level is high, and compared to special mask A and special mask B, even when banding occurs, the change in the usable rate of nozzle 14 is smaller. In the case of special mask A shown in Figure 13B, the dryness resistance level is medium, so it is more effective as a countermeasure against dryness than the normal mask. However, as can be seen by comparing the graphs on the right of Figures 13A and 13B, when banding occurs, the change in the usable rate of nozzle 14 is larger than with the normal mask, raising concerns about a decrease in image quality.

[0117] In the case of special mask C shown in Figure 13C, the dryness resistance level is high, so it is the most effective in terms of preventing dryness. However, as can be seen by comparing the graph on the right of Figure 13C with the graphs on the right of Figures 13A and 13B, when banding occurs, the change in the nozzle 14 usage permission rate is larger than with the other masks, raising concerns about a significant degradation in image quality.

[0118] For these reasons, in Modification 5, the mask that was initially selected from the perspective of a dryness countermeasure is reviewed from the perspective of a banding countermeasure. Then, when the degree of banding is above a certain level (when it is easily noticeable), the mask is switched to one with a one-level lower dryness countermeasure level (in other words, a mask with a one-level higher banding countermeasure level). This makes it possible to implement a good balance between dryness countermeasures and banding countermeasures.

[0119] In the above description, the liquid ejection device 1 is exemplified as one in which the same type of liquid is ejected using two ejection heads 10A, 10B and one seam region is formed between these two ejection heads 10A, 10B. However, the present disclosure is not limited to this. For example, the liquid ejection device according to the present disclosure can also be applied to a liquid ejection device in which the same type of liquid is ejected using three or more ejection heads and a total of two or more seam regions are formed between these three or more ejection heads. [Industrial Applicability]

[0120] The present disclosure can be applied to a liquid ejection device that ejects liquid, a liquid ejection method, and a liquid ejection program. [Explanation of symbols]

[0121] 1 Liquid discharge device 10 Discharge head 10A First ejection head 10B Second ejection head 11 Color Head 11a 1st color head 11b 2nd color head 11c Color Joint Area 12 Special Head 12a First feature head 12b 2nd special color head 12c Special color joint area 13 White Head 13a First white head 13b 2nd white head 13c White background seam area 14 nozzles 14a No. 1 nozzle 14b Second nozzle 15a, 15b nozzle array 17 nozzle rows 22 Conveyor equipment 23 Mobile Devices 40 Control device 55 Temperature Sensor 56 Humidity Sensor

Claims

1. a first ejection head having a plurality of first nozzles for ejecting liquid; a second ejection head having a plurality of second nozzles for ejecting the liquid; a conveying device that conveys a recording medium in a conveying direction relative to the first ejection head and the second ejection head; a moving device that moves the first ejection head and the second ejection head in a movement direction that intersects with the transport direction; a control device; the first ejection head and the second ejection head are arranged such that, in a predetermined seam region, positions of some of the first nozzles among the plurality of first nozzles and positions of some of the second nozzles among the plurality of second nozzles overlap in the transport direction; The control device a risk acquisition process for acquiring information regarding a drying risk of the liquid in each of the first nozzles and the second nozzles; a mask selection process that selects one mask according to the drying risk from among a plurality of masks that are provided according to differences in the ratios, the mask determining a rate at which the number of nozzles used to eject liquid among the plurality of first nozzles that are aligned in the movement direction among the portion of first nozzles increases in one direction of the transport direction, and a rate at which the number of nozzles used to eject liquid among the plurality of second nozzles that are aligned in the movement direction decreases in one direction of the transport direction; a printing process for printing using the selected mask based on the print job; A liquid ejection device that performs the above.

2. the control device, in the mask selection process, selects a mask having a smaller ratio as the risk of drying increases; The liquid ejection device according to claim 1 .

3. The control device performing a flushing process to discharge liquid from the first nozzle and the second nozzle; In the mask selection process, if a predetermined first period has elapsed since the previous flushing process, a mask with a smaller ratio is selected than if the first period has not elapsed. The liquid ejection device according to claim 2 .

4. the masks include at least a normal mask and a special mask in which the first ratio and the second ratio are smaller than those of the normal mask; In the mask selection process, if a printing period using the normal mask has elapsed a predetermined second period, the control device selects the special mask instead of the normal mask. The liquid ejection device according to claim 2 .

5. The control device a pass printing process is executed in which the moving device moves the first ejection head and the second ejection head in the movement direction while ejecting the liquid, and the transporting device transports the recording medium in the transport direction; In the mask selection process, when the ejection amount of the liquid in the next pass is equal to or greater than a predetermined first threshold, a mask having a smaller ratio is selected than when the ejection amount of the liquid is less than the first threshold. The liquid ejection device according to claim 2 .

6. The control device a pass printing process is executed in which the moving device moves the first ejection head and the second ejection head in the movement direction while ejecting the liquid, and the transporting device transports the recording medium in the transport direction; In the mask selection process, when the droplet ejection amount in the next pass is less than a predetermined second threshold, a mask with a smaller ratio is selected than when the droplet ejection amount is equal to or greater than the second threshold. The liquid ejection device according to claim 2 .

7. The control device a pass printing process is executed in which the moving device moves the first ejection head and the second ejection head in the movement direction while ejecting the liquid, and the transporting device transports the recording medium in the transport direction; the mask selection process is performed before the start of the pass printing process for one pass during execution of the print job or after the end of the pass printing process; The liquid ejection device according to claim 2 .

8. a temperature sensor that detects information about the temperatures around the first ejection head and the second ejection head; In the mask selection process, the control device selects a mask having a smaller ratio when the temperature is equal to or higher than a predetermined threshold value than when the temperature is below the threshold value. The liquid ejection device according to claim 2 .

9. a humidity sensor that detects information about the humidity around the first ejection head and the second ejection head; In the mask selection process, the control device selects a mask with a smaller ratio when the humidity is less than a predetermined threshold value than when the humidity is equal to or greater than the threshold value. The liquid ejection device according to claim 2 .

10. the first ejection heads include a first color head that ejects process color ink as the liquid, and a first special color head that ejects special color ink as the liquid, the second ejection heads include a second color head that ejects process color ink as the liquid, and a second special color head that ejects special color ink as the liquid, the seam region includes a color seam region between the first color head and the second color head, and a special color seam region between the first special color head and the second special color head, When the print job includes the printing process in the spot color seam region, the control device selects a mask with a smaller ratio in the mask selection process than when the print job does not include the printing process in the spot color seam region. The liquid ejection device according to claim 1 .

11. the control device, when the rate of small droplets among small droplets and large droplets of the liquid ejected in the seam region during the printing process is equal to or greater than a predetermined threshold, selects a mask in which the rate is smaller than when the rate is less than the threshold. The liquid ejection device according to claim 2 .

12. The control device performing a banding detection process to detect banding in a printed image due to a deviation in the relative position of the first ejection head and the second ejection head; In the mask selection process, when the degree of banding detected from the print image in the seam region is equal to or greater than a predetermined threshold, a mask having a larger ratio is selected than when the degree of banding is less than the threshold. The liquid ejection device according to claim 1 .

13. The control device executing a non-ejection detection process for detecting whether or not a non-ejection nozzle exists among the part of the first nozzles and the part of the second nozzles; In the mask selection process, when a non-ejecting nozzle is detected in either one of the first nozzles or the second nozzles, a mask that uses only the other nozzle is selected for the seam region. The liquid ejection device according to claim 1 .

14. the control device selects a mask that uses only the other nozzle before executing the printing process; The liquid ejection device according to claim 13.

15. a liquid ejection method using a liquid ejection device comprising: a first ejection head having a plurality of first nozzles for ejecting a liquid; a second ejection head having a plurality of second nozzles for ejecting the liquid; a transport device that transports a recording medium in a transport direction relative to the first ejection head and the second ejection head; a moving device that moves the first ejection head and the second ejection head in a movement direction intersecting the transport direction; and a control device, wherein the first ejection head and the second ejection head are arranged such that positions of some first nozzles of the plurality of first nozzles and positions of some second nozzles of the plurality of second nozzles overlap in the transport direction in a predetermined joint region, execute a risk acquisition process for acquiring information about a drying risk of the liquid in each of the first nozzles and the second nozzles; a mask that determines a rate at which the number of nozzles used to eject liquid among the plurality of first nozzles aligned in the movement direction among the portion of first nozzles increases in one direction of the transport direction, and a rate at which the number of nozzles used to eject liquid among the plurality of second nozzles aligned in the movement direction decreases in one direction of the transport direction, and a mask selection process is executed to select one mask according to the drying risk from among a plurality of masks that are provided according to differences in the rate; Execute a print process that performs printing using the selected mask based on the print job; Liquid dispensing method.

16. a liquid ejection program to be executed by a computer in a liquid ejection apparatus comprising: a first ejection head having a plurality of first nozzles for ejecting liquid; a second ejection head having a plurality of second nozzles for ejecting the liquid; a transport device that transports a recording medium in a transport direction relative to the first ejection head and the second ejection head; a moving device that moves the first ejection head and the second ejection head in a movement direction intersecting the transport direction; and a control device, wherein the first ejection head and the second ejection head are arranged such that positions of some first nozzles of the plurality of first nozzles and positions of some second nozzles of the plurality of second nozzles overlap in the transport direction in a predetermined seam region, The computer a risk acquisition means for acquiring information regarding a risk of the liquid in each of the first nozzles and the second nozzles drying; a mask selection means for determining a rate at which the number of nozzles used to eject liquid among the plurality of first nozzles aligned in the movement direction among the portion of first nozzles increases in one direction of the transport direction, and a rate at which the number of nozzles used to eject liquid among the plurality of second nozzles aligned in the movement direction among the portion of second nozzles decreases in one direction of the transport direction, and for selecting one mask in accordance with the drying risk from among a plurality of masks according to differences in the rate; a printing means for printing using the selected mask based on the print job; A liquid dispensing program that functions as a

Images